Self-Powered Transmitter No Batteries Required – Press the button to generate electricity, eliminating battery replacement Wireless Technology – 433.92MHz frequency for reliable transmission Transmission Range – Up to 100 meters in open area Compact Design – Φ55×20mm, easy to mount on any door frame Receiver with Rich Features 36 Built-in Ringtones – Choose from a variety of melodies 8 Adjustable Volume Levels – From mute to …